This invention relates to a connection method and structure for connecting covered wires with each other or connecting a covered wire to another member.
As a conventional connection structure for this kind of covered wires, an art proposed by this inventor (see Japanese Laid-Open Patent Application No. 7-320842) will be described.
For connecting two covered wires the outer periphery of which is coated with a cover portion made of resin, at their intermediate connection portions, a pair of resin chips which are of resin material, a horn for producing ultrasonic vibration, and an anvil for supporting the covered wires and resin chips at the time of connection are utilized. The anvil includes a base stand and a support portion projecting from the base stand. The support portion is designed in a substantially cylindrical shape. The support portion has a bore portion which is opened at the opposite side to the base stand side. Two pairs of grooves are formed on the peripheral wall of the support portion so as to cross with each other substantially at the center of the bore portion. The four grooves are formed so as to open on the same side as the bore portion, extending along the projection direction of the support portion and intercommunicate with one another through the bore portion.
The pair of resin chips are designed in a disc shape having a slightly smaller outer diameter than the diameter of the bore portion of the anvil. Furthermore, an end face of a head portion of the horn is designed in a disc shape having an outer diameter which is substantially equal to or slightly smaller than that of the resin chips.
The respective resin chips have solder as soldering material. The solder is embedded substantially in the center of the bottom/top surface such that a circular top face thereof is flush with the bottom/top surface (melting surface) of the upper and lower resin chips.
In order to connect the two covered wires to each other, both of the covered wires are overlapped with each other at the connection portion thereof and the overlapped connection portions are pinched through a solder by the pair of resin chips from the upper and lower sides of the connection portions. Specifically, one of the resin chips (the resin chip at the lower side) is inserted into the bore portion of the anvil such that the melting surface thereof is directed upward. Then, one covered wire is inserted into the pair of confronting grooves from the upper side of the inserted resin chip. Then, the other covered wire is inserted into the other pair of the confronting grooves. Finally, the other (upper side) resin chip is inserted such that the melting surface is directed downward. The covered wires are arranged in the bore portion so that the respective connection portions thereof cross each other at the center of the bore portion. Through this arrangement, the connection portions of the covered wires are pinched substantially at the center of the melting surfaces of the upper and lower resin chips, respectively, in the (vertical) direction.
Subsequently, the cover portions at the connection portions of the covered wires are melted so as to be dispersed by ultrasonic vibration. Furthermore, the conductive wire portions (core) of the covered wires are conductively contacted with each other at the connection portion by pressing the covered wires from the outside of the resin chips. Thereafter, the pair of the resin chips are mutually melt-fixed at the melting surfaces to seal the connection portion.
Specifically, the head portion of the horn is inserted into the bore portion from the upper side bore portion from the upper side of the finally-inserted upper (other) resin chip and placed on the upper resin chip to excite and press the connection portions of the covered wires from the outside of the upper and lower resin chips between the horn and the anvil. The cover portions are first melted and the conductive wire portions of the covered wires are exposed at the connection portion between the resin chips. At this time, the melted cover portions are extruded from the center side of the resin chips toward the outside thereof because the connection portions are pressed from the upper and lower sides, so that the conductive wire portions are more effectively exposed and surely conductively contacted with each other. Like the press direction, the direction of the excitation of the connection portions is set to be coincident with the overlapping direction of the covered wires, so that the action of extruding the melted cover portions from the center side of the resin chips to the outside thereof is promoted.
When the pressing and exciting operation on the connection portions is continued after the melting of the cover portions, the resin chips are melted and the facing melting surfaces of the resin chips are melt-fixed to each other. In addition, the outer peripheral surface portions of the cover portions which are adjacent to the conductively contacted conductive wire portions and the resin chips are melt-fixed. With this operation, the outer peripheral portions of the conductively-contacted conductive wire portions are kept to be coated with the resin chips.
The solder provided in the resin chips is melted by eat generated when the resin chips are melted. Consequently the conductive wire portions of the conductively contacted covered wires are soldered at the connection portions in the resin chips. As a result, a higher electric performance can be obtained at the connection portions thereby further stabilizing the conductive characteristic.
However, in this connection structure, solder must be melted accurately at the same timing in a series connecting process as when the cover portion is melted, such that the conductive wire portion is exposed and contacted with each other. Thus, the solder needs to be buried inside of the resin chips without being exposed through melting surfaces of resin chips, respectively. When burying the solder inside of the resin chips, during the production process of the resin chips, a special treatment for sealing opening portions, for the burying with resin material, is needed after the solder is buried in the resin chips. Thus, increase in cost of the resin chips cannot be avoided.
Further, to melt solder accurately at the required timing, detailed setting and management of a position of the solder in the resin chips and ultrasonic melting condition (particularly temperature) must be conducted. Thus, conductive connecting procedure becomes complicated and is such an intrinsic effect on this technology that conductive connection performed by a simple method may be lost.
Further, the solder needs to contain a mixture of chemical active substance (flux) for improving a leaking characteristic for core wires comprising the conductive wire portion. In this technology which solders the connection portions and simultaneously seals it, this kind of flux needs to be contained in the resin chips. Thus, there is a fear that the connection portions may corrode due to flux, so that conversely, reliability relating to electrical connecting performance may be reduced.